Method of controlling bump printing apparatus

ABSTRACT

A method of controlling a bump printing apparatus includes securing a board having air holes therein to a printing table by vacuum suction using suction nozzles; bringing a mask into close contact with the board; printing solder bumps by compressing and moving a solder paste across an upper surface of the mask using a squeegee; spraying air through spray nozzles to separate the mask from the board; and terminating air spraying using the spray nozzles and terminating air suction using the suction nozzles to remove the board.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 12/588,047, filed onOct. 1, 2009, which claims the priority of Korean Patent Application No.10-2009-0041644 filed on May 13, 2009, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein byreference.

BACKGROUND

1. Field

The present invention relates to a bump printing apparatus and a methodof controlling the same, and more particularly, to a bump printingapparatus and a method of controlling the same that can increase theprintability of solder bumps being printed on a board.

2. Description of the Related Art

In general, flip chip bonding, tape automated bonding and wire bondingare being used to interconnect external boards, such as printed circuitboards (PCBs) or wafer level packages (WLPs), to chips.

Among them, flip chip bonding has been widely used to manufactureportable electronic products, since this method increases the number ofpads per unit area.

According to flip chip bonding, solder bumps are formed on a wafer inorder to appropriately bond chips and external circuitry. Particularly,a technique for manufacturing solder bumps has been developed to formsolder bumps having appropriate conductivity, uniform lengths and finepitches.

According to this solder bump forming technique for flip chip bonding,the characteristics of solder bumps and an application range thereof aredetermined according to the materials used to form solder bumps.Examples of the solder bump forming technique may include a solderingmethod of contacting pad electrodes to solder, a screen printing methodof forming solder bumps on pad electrodes by screen printing andreflowing the solder bumps, a solder ball reflow method of mountingsolder balls onto pad electrodes and reflowing the mounted solder balls,and a plating method of performing solder plating on pad electrodes.

Among them, a screen printing method has been widely used to form solderbumps in that the process of forming solder bumps in this manner issimple, manufacturing costs are low, and bumps of desired metallicmaterial can be formed.

Furthermore, a snap-off method of separating a mask and a board fromeach other after finishing screen printing includes a mask snap-offmethod in which a PCB is fixed and a mask is lifted to separate the maskand the PCB and a table snap-off method in which a mask is fixed and atable having a PCB mounted thereon is lowered to separate the mask andthe PCB.

However, according to these methods, when the mask and the PCB areforcibly separated from each other, the mask sags and thus the speeds atwhich the mask and the board are separated vary according to portions.As a result, variations in the shapes of solder bumps and variations inthe amounts of solder pastes being printed may occur.

Therefore, bump defects, such as the spreading of solder pastes, shortcircuits and missing bumps, in which bumps are not formed, occur toreduce the printability of bumps, which may reduce the reliability ofprinted circuit boards.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a bump printing apparatusand a method of controlling the same that can increase the printabilityof solder bumps by allowing for the easy withdrawal of solder pastes soas to maintain the shapes of bumps and increase the reliability of aboard by preventing the generation of bump defects.

According to an aspect of the present invention, there is provided abump printing apparatus including: a printing table onto which a boardis mounted; a mask making close contact with the board and printingsolder bumps on the board by separating the mask from the board after aprinting operation; and air nozzles provided within the printing tableand providing air suction to bring the board into close contact with theprinting table and spraying air to separate the mask from the board.

The bump printing apparatus may further include the air nozzlesincluding a plurality of suction nozzles providing air suction and aplurality of spray nozzles spraying air, the suction nozzles and thespray nozzles arranged along an upper surface of the printing table.

The spray nozzles may generate air pressure between the mask and theboard in close contact with each other under vacuum so that the mask andthe board are separated from each other.

The spray nozzles may spray air so that the mask is separated from theboard while maintaining a horizontal state with respect to the board.

The spray nozzles may be inclined so that air is sprayed in a directionfrom a central portion of the printing table toward the outside thereofor the inside thereof.

The board may have air holes formed therethrough so that air beingsprayed through the air nozzles passes through the board and movesupward from the board.

The bump printing apparatus may further include a control unitcontrolling the air nozzles.

According to another aspect of the present invention, there is provideda method of controlling a bump printing apparatus, the method including:securing a board having air holes therein to a printing table by vacuumsuction using suction nozzles; bring the mask into close contact withthe board; printing solder bumps by compressing and moving a solderpaste across an upper surface of the mask using a squeegee; spraying airthrough spray nozzles to separate the mask from the board; andterminating air spraying using the spray nozzles and terminating airsuction using the suction nozzles to remove the board.

The securing of the board may further include aligning the board so thatthe air holes are arranged at locations corresponding to the spraynozzles of the printing table.

The bringing of the mask into close contact with the board may furtherinclude providing air suction through the suction nozzles.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1A is a perspective view schematically illustrating a bump printingapparatus according to an exemplary embodiment of the present invention;

FIG. 1B is a cross-sectional view schematically illustrating the bumpprinting apparatus, shown in FIG. 1A;

FIG. 2 is a plan view illustrating a printing table including suctionnozzles and spray nozzles of the bump printing apparatus, shown in FIGS.1A and 1B;

FIG. 3 is a cross-sectional view illustrating the printing table, shownin FIG. 2;

FIG. 4A is a cross-sectional view schematically illustrating anotherexample of the spray nozzles of the printing table, shown in FIG. 3;

FIG. 4B is a plan view schematically illustrating another example of thespray nozzles of the printing table, shown in FIG. 3;

FIG. 5A is a cross-sectional view schematically illustrating anotherexample of the spray nozzles of the printing table, shown in FIG. 3;

FIG. 5B is a plan view schematically illustrating another example of thespray nozzles of the printing table, shown in FIG. 3;

FIG. 6A is a plan view schematically illustrating a state in which aboard and a mask are mounted on the printing table, shown in FIGS. 2Aand 2B;

FIG. 6B is an enlarged plan view taken along the line y-y of FIG. 6A;and

FIGS. 7A through 7E are schematic views illustrating a printing processbeing performed using a method of controlling a bump printing apparatusaccording to an exemplary embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 1A is a perspective view schematically illustrating a bump printingapparatus according to an exemplary embodiment of the invention. FIG. 1Bis a cross-sectional view schematically illustrating the bump printingapparatus shown in FIG. 1A. FIG. 2 is a plan view illustrating aprinting table including suction nozzles and spray nozzles of the bumpprinting apparatus, shown in FIGS. 1A and 1B. FIG. 3 is across-sectional view illustrating the printing table, shown in FIG. 2.

FIG. 4A is a cross-sectional view schematically illustrating anotherexample of the spray nozzles of the printing table, shown in FIG. 3.FIG. 4B is a plan view schematically illustrating another example of thespray nozzles of the printing table, shown in FIG. 3. FIG. 5A is across-sectional view schematically illustrating another example of thespray nozzles of the printing table, shown in FIG. 3. FIG. 5B is a planview schematically illustrating another example of the spray nozzles ofthe printing table, shown in FIG. 3. FIG. 6A is a plan viewschematically illustrating a state in which a board and a mask aremounted on the printing table, shown in FIGS. 2A and 2B. FIG. 6B is anenlarged plan view taken along the line of FIG. 6A.

Referring to FIGS. 1 through 6, a bump printing apparatus 1 according tothis embodiment includes a printing table 10, a mask 20 and air nozzles30.

The printing table 10 is a jig member that is used to secure a board bto be mounted onto an upper surface thereof so as to perform screenprinting to print solder bumps 60.

As shown in FIGS. 1A and 1B through 6A and 6B, the printing table 10generally has a rectangular shape corresponding to a shape of the boardb. However, the present invention is not limited thereto.

As for the board b, general boards, such as a ceramic board and aprinted circuit board (PCB), formed of resin materials, including rigidand flexible PCBs, may be used.

Here, a plurality of air holes h are formed through the board b so thatair being sprayed through the air nozzles 30 passes through the board band moves upward from the board b.

The air holes h are formed so that air being sprayed from the printingtable 10 separates the mask 20 in close contact with the board b withoutbeing interrupted by the board b. A detailed description of the airholes h will be described in detail below.

The mask 20 is provided on an upper surface of the board b that ismounted on the printing table 10. The mask 20 has pattern holes 21,arranged in a predetermined pattern, and is supported by a jig 22.

The mask 20 makes close contact with and is secured to the upper surfaceof the board b. After a solder paste p is compressed and moved using asqueegee s in order to print the solder bumps 60, the mask 20 isseparated from the board b again to thereby form the solder bumps 60 onthe board b.

At this time, as a vacuum is substantially created between the mask 20and the board b, the mask 20 and board b are not misaligned during ascreen printing process to thereby accurately print the solder bumps 60at design positions.

The mask 20 may be a general metal mask. However, the present inventionis not limited thereto. A mask of another material may be provided asthe mask 20.

The air nozzles 30 are provided within the printing table 10, provideair suction so that the board b makes close contact with the printingtable 10 and spray air so that the mask 20 is separated from the boardb.

As shown in FIGS. 1A and 1B through FIGS. 6A and 6B, the air nozzles 30include a plurality of suction nozzles 31 providing air suction, and aplurality of spray nozzles 32 spraying air, which are arranged along theupper surface of the printing table 10.

The suction nozzles 31 provide air suction at constant pressure tothereby secure the board b mounted on the upper surface of the printingtable 10, by vacuum suction.

Meanwhile, the spray nozzles 32 spray air between the mask 20 and theboard b and generate air pressure between the mask 20 and the board b inclose contact with each other under vacuum to thereby separate the mask20 and the board b from each other.

In particular, the spray nozzles 32 spray air while adjusting thepressure of air being sprayed so that the mask 20 can be separated fromthe board b while maintaining the horizontal state.

That is, in order to separate the board b and the mask 20 from eachother when finishing the printing process, although the mask 20 sags,the mask 20 is not forcibly separated like the related art, but the mask20 is separated from the board b while maintaining the horizontal stateby air pressure caused by air blowing, so that the solder paste p can beeasily withdrawn from the pattern holes to thereby form the solder bumps60.

Furthermore, as shown in FIGS. 4A and 4B, the spray nozzles 32 may beinclined at a predetermined angle θ so that the spray nozzles 32 canspray air in a radial direction from the center of the printing table 10toward the outside thereof.

Here, as shown in FIGS. 4A and 4B, while the spray nozzles 32, locatedat the center portion of the mask 20 that coincides with the center ofthe mask 20, may be arranged in a vertical direction perpendicular tothe upper surface of the printing table 10, the spray nozzles 32 may beinclined at the predetermined angle a toward the outside of the printingtable 10 as the spray nozzles 32 get distant from the central portion.That is, the spray nozzles 32 of the printing table 10 may have a radialshape.

Therefore, although the mask 20 generally sags toward the centralportion, air is sprayed in a direction corresponding to the sagging mask20, which facilitates maintaining the horizontal state of the mask 20.

Further, as shown in FIGS. 5A and 5B, the spray nozzles 32 may beinclined at a predetermined angle θ so that air is sprayed into aconical form toward the central portion of the printing table 10.

Contrary to the above-described radial shape, the spray nozzles 32 areinclined toward the central portion of the printing table 10 as thespray nozzles 32 get distant from the central portion of the printingtable 10.

Here, air is sprayed in a direction facing the sagging mask 20 so thatair is mainly sprayed onto the most severe sagging portion of the mask20, so that the horizontal state of the mask 20 can be easilymaintained.

The locations of inlets of the spray nozzles 32 that are exposed to theupper surface of the printing table 10 are constant both in the case inwhich the spray nozzles 32 are arranged in a perpendicular direction tothe printing table 10 and the case in which the spray nozzles 32 areinclined at the predetermined angle θ.

The locations of the air holes h provided through the board b correspondto those of the inlets of the spray nozzles 32.

Therefore, even when the board b is mounted onto the printing table 10,since the spray nozzles 32 and the air holes h overlap and communicatewith each other, the inlets of the spray nozzles 32 are not blocked bythe board b. As a result, air being sprayed through the spray nozzles 32can pass through the air holes h and move upward from the board b.

While the spray nozzles 32 spray air to separate the mask 20, the spraynozzles 32 provide air suction as the suction nozzles 31 do so that themask 20 can be brought into closer contact with the board b.

That is, when the solder bumps 60 are printed, the spray nozzles 32provide air suction as the suction nozzles 31 do to thereby bring themask 20 into closer contact with the upper surface of the board b. Afterthe process of printing the solder bumps 60 is completed, the spraynozzles 32 spray air to separate the mask 20 from the board b.

As such, when air suction is provided by the spray nozzles 32 to bringthe mask 20 into close contact with the board b by vacuum suction, thegeneration of gaps between the mask 20 and the board b can be prevented.

The suction nozzles 31 and the spray nozzles 32 are connected to pipes33 and 34, respectively, which do not communicate with each other andseparately guide the flow of air. The pipes 33 and 34 are connected toair pumps 41 and 42, respectively, which are provided outside theprinting table 10.

The air pumps 41 and 42 are controlled independently of each other sothat air suction through the suction nozzles 31 and air suction andspraying through the spray nozzles 32 are performed independently ofeach other.

The air nozzles 30, which are controlled according to the drivingoperation of the air pumps 41 and 42, can be more accurately controlledby a control unit 50 that is separately provided.

A method of controlling a bump printing apparatus according to anexemplary embodiment of the invention will be described in detail.

FIGS. 7A through 7E are schematic views illustrating a printing processbeing performed using a method of controlling a bump printing apparatusaccording to an exemplary embodiment of the invention.

Referring to FIG. 7A, the board b for printing the solder bumps 60 isplaced on the upper surface of the printing table 10 having theplurality of suction nozzles 31 and the plurality of spray nozzles 32.

The plurality of air holes h are formed in the board b. When the board bis placed on the printing table 10, the board b is arranged so that theair holes h and the spray nozzles 32 overlap and communicate with eachother.

The air pump 41, connected to the suction nozzles 31, is then operatedto provide air suction through the suction nozzles 31 so that the boardb is secured to the printing table 10 by vacuum suction.

Then, as shown in FIG. 7B, the mask 20, which has the pattern holes 21arranged in the predetermined pattern and is supported by the jig 22, isbrought into close contact with the board b.

Here, the air pump 42, connected to spray nozzles 32, is operated toprovide air suction so that the mask 20 can make closer contact with theboard b.

As such, while the board b and the mask 20 are in surface contact witheach other, the solder paste p fills in the pattern holes 21 of the mask20 to perform a printing process by compressing and moving the solderpaste p across the upper surface of the mask 20 using the squeegee s, asshown in FIG. 7C.

After the printing process is completed, as shown in FIG. 7D, the airpump 42, connected to the spray nozzles 32, is operated to spray airthrough the spray nozzles 32 so that the mask 20 and the board b areseparated from each other.

Here, since the mask nozzles 32 communicate with the air holes h of theboard b, air, sprayed through the spray nozzles 32, may pass through theair holes h and move towards the upper surface of the board b.

Therefore, air pressure causing separation of the mask 20 and the boardb from each other is generated by air being introduced between the boardb and the mask 20.

Here, the suction nozzles 31 continuously provide air suction so as tokeep the board b secured to the printing table 10.

Then, as shown in FIG. 7E, after the mask 20 is separated from the boardb, the spraying of air through the spray nozzles 32 is terminated, andair suction through the suction nozzles 31 is terminated, so that theboard b is removed from the printing table 10.

A new board b is arranged on the printing table 10, and a printingprocess continues to be performed on the board b.

The air pumps 41 and 42, connected to the suction nozzles 31 and thespray nozzles 32, respectively, may be controlled independently of eachother by the control unit 50. In particular, the control unit 50controls the pressure of air sprayed through the spray nozzles 32 so asto maintain the horizontal state of the mask 20.

Therefore, elaborate management to separate the sagging mask 20 from theboard such as that in the related art is unnecessary.

As such, the mask 20 is separated from the board b by air pressurecaused by air blowing while maintaining the horizontal state, so thatthe solder paste can be easily withdrawn from the pattern holes toeasily print the solder bumps 60.

Therefore, defects of the solder bumps 60 can be effectively preventedto increase printability and yield, which may increase the reliabilityof the board b.

As set forth above, according to exemplary embodiments of the invention,the bump printing apparatus can prevent the generation of defects insolder bumps and allows for the easy withdrawal of solder pastes throughpattern holes to form solder bumps to increase printability and yield,thereby increasing the reliability of a circuit board.

Furthermore, elaborate management to separate a mask and a board such asthat in the related art is unnecessary, thereby facilitating amanufacturing process and thus improving apparatus productivity, andapplicability increases because of a simplified configuration thereof.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A method of controlling a bump printing apparatus, the methodcomprising: securing a board having air holes therein to a printingtable by vacuum suction using suction nozzles; bringing a mask intoclose contact with the board; printing solder bumps by compressing andmoving a solder paste across an upper surface of the mask using asqueegee; spraying air through spray nozzles to separate the mask fromthe board; and terminating air spraying using the spray nozzles andterminating air suction using the suction nozzles to remove the board.2. The method of claim 1, wherein the securing of the board furthercomprises aligning the board so that the air holes are arranged atlocations corresponding to the spray nozzles of the printing table. 3.The method of claim 1, wherein the bringing of the mask into closecontact with the board further comprises providing air suction throughthe suction nozzles.